Timed insertion bridge

ABSTRACT

I disclose an arrangement for holding up a connection from the called end in a telephone switching system. Gradual insertion of holding bridges across the transmission paths of all switches serving a particular subscriber line eliminates acoustical disturbances. Responsive to a called subscriber signal, a bridge containing the emitter-collector path of a transistor is placed across the transmission paths by slowly biasing the transistor into conduction.

- United States Patent [72] Inventor Donald C. Pildnton [56] References Cited Mmchem UNITED STATES PATENTS [211 P 2,855,469 10/1958 White 179/1152 [221 PM 1968 3 131 710 6/1964 DO 1 179 ye /l8(.6l) [451 1971 2 996 629 8/1961 Rhodes 328/97 x [73] Assignee Bell Telephone Laboratories, Incorporated Murray Hill, Berkeley Heights, NJ. Primary Examiner-Kathleen H. Claffy Assistant Examiner-Jan S. Black Attorneys-R J. Guenther and James Warren Falk ABSTRACT: I disclose an arrangement for holding up a con- [54] g g i nection from the called end in a telephone switching system. Gradual insertion of holding bridges across the transmission [52] US. Cl "91175.2 C, paths of all switches serving a particular subscriber line 179/ l 8 PH, 179/ 1 MN eliminates acoustical disturbances. Responsive to a called sub- ISI lnt.Cl "04m 3/22 scriber signal, a bridge containing the emitter-collector path [50] Field of Search 179/1 MN of a transistor is placed across the transmission paths by slowly 5.5, l8.6l, 2712,1752 C biasing the transistor into conduction.

ZTRA-IIO PATENIEB AUG! 7 IB'II SHEET 1 BF 2 BRIDGE Isl/Z CONNECTOR ATTORNEY TIMED INSERTION BRIDGE BACKGROUND OF THE INVENTION This invention relates to inserting bridging elements across transmission paths in telephone systems and, more particularly, to arrangements for enabling the origins of calls to be traced. v I

In automatic telephone systems it is sometimes desirable to be able to maintain a connection to permit tracing a call to its origin. For example, subscribers may be annoyed, insulted, and even threatened by anonymous and often obscene calls, sometimesreferred to as nuisance calls. Numerous arrangements have been devices in the prior art whereby such calls may be trapped, traced, and the calling line identified. Many of these arrangements require that the maintenance of the connection be done from the called end, since the calling line is not known.

In step-by-step telephone systems, a connection may be maintained despite the calling party going on-hook by keeping energized the calling party supervisory relay in the connector, simulating the receiver off-hook condition of the calling party. An example of an arrangement for performing such a function is disclosed in US. Pat. No. 3,137,770, entitled Telephone Call Holding Arrangement, issued on June 16, 1964 to ME. Doyle. However, a called customer's line is multipled to many connectors and each connector serves many customers. Since it is not initially known which'connector is actually part of the connection to be maintained, the calling party supervisory relays in all of the connectors serving the customer whose called connections are to be maintained must be locked up. In the aforementioned Doyle patent, this is accomplished by a polarity sensitive bridge which is automatically inserted when the called party supervisory relay in the connector is energized, this relay reversing the battery across the line in response to the called 'party going off-hook. In other prior art arrangements, the called party may be equipped with a signaling device whereby-a trace can be requested. In these arrangements, locking up the called party supervisory relay has been done by inserting holding bridges across the transmission paths of all the connectors through the closure of a relay contact when the called party requests calling line identification. In the latter type of arrangement, as a result of this sudden insertion of the bridges, acoustical disturbances, or clicks are heard in the talking-paths. These clicks are undesirable, since innocent conversations may be taking place on others of the ,connectors which are bridged, and undue annoyance to telephone customers is to be avoided whenever possible SUMMARY OF THE INVENTION 7 device, the device being initially in a nonconductive state.

Each of these timers is actuated upon the called line requesting calling line identification. This actuationcauses the timer to slowly increase the conductivity of the device,

thereby insertingthe bridge without creating any acoustical disturbances.

DESCRIPTION OFTI-IE DRAWING FIGS. land withFIG. I placed tothe left of-FlG. 2, de-

pict an illustrative em'bodimentofthe present invention in a step-by'step telephone switching system wherein a called party may request a manual trace uponreceipt of a nuisance call.

GENERAL DESCRIPTION -The drawing shows the connections at the called end in a step-by-step telephone switching system. Station sets 200 and 201, FIG. 2, are representative of the station sets connected to connectors 100 through 109, FIG. 1. In such a system, each particular station set is connected to the same level on the output banks of all connectors. Station sets I10 and 111, FIG. 1, are shown as being the originators of calls to station sets 200 and 201, respectively, but only the portions of the connections necessary for an understanding of my invention have been shown. r

Assuming that the customer at station set 200 has been the recipient of annoying telephone calls, Called ustomer Supervision'Circuit 210, FIG. 2, is inserted in the line of station set 200 at the central office, and bridges: 120 through 129, FIG. 1, are connected across the transmission paths of connectors 100 through 109, these connectors being all the connectors which serve station set 200.

Oneof the functions of circuit 210 is to distinguish between a call terminating at station set 200 and a call being originated by station set 200. If a call is originated by station set 200, circuit 210 performs no circuit operations with regard to maintaining the connection. However, if circuit 210 detects that a call is terminating at station set 200, circuit 210 is enabled to receive a calling line identification request from station set 200. Upon receipt of this request, circuit 210 actuates timers which cause bridges 120 through 129 to be gradually inserted across the transmission paths of connectors 100 through 109 without any acoustical disturbances. Thus, the parties conversing over connectors 100 through 109 are unaware of any bridging. When these bridges are inserted across the transmis sion paths of the connectors, the calling party supervisory relays in connectors 100 through .109 are held operated independent of any action taken by the calling customer. The continued operation of these relays maintains the sleeve control relays in an operated state, thereby grounding the sleeve leads going back toward the callingends and keeping the connections locked :up. Alarm circuits, no shown, are actuated in the central office to notify central office personnel that a manual trace isrequired. Afterthemanual trace is completed, circuit 210 is released, by circuitry not shown and bridges 120 through 129 are removed from the transmissionpaths of connectors 100 through 109.

DETAILEDDESCRIPTION SI, the sleeve lead, which maintains the connection from station' set 110 upto connector so long as relay A remains energized. A ground is also applied to conductorSZ, and through the output bank of connector 100 to conductor S3, by circuitry, notshown, in connector I00, operating relay 28in CalledCustomer'Supervision Circuit2l0.

When'station set 200 goes off-hook in response to this call, relay D in'connector 100 is operatedovcr a path from negative battery through the right-handrwinding of relay D, conductor T2, through theoutputbanlt of connector 100;conductor'T3, normally closedzcontacts 20R--l, the upper'winding of relayZL,stationset'200; the lower winding'ofrelay 2L, normally closed contacts 20R-2, conductor R3, through: the output bank of connector 100, conductor R2,.andthe lefthand winding of relay D to ground. This same'path also causes relay IL in Called Customer "Supervision Circuit '210 to become energized.

As mentioned above, relay 2S previously been operated.

The operation of relay 2S prior'to the operation of relay 2L operates responsive only to thev aforementioned order of operation of relays description.

' The operation of relay 25 before relay 2L allowsrelay 2SL to operate over a path from ground through make contacts 2S-1, normally closed contacts ZL-l, and the winding or relay 28L to'negative battery. The subsequent operation of relay 2L MAlNTAINS RELAY v 2S1. operated over the path from ground through make contacts 28-], make contacts ZL-l, make contacts ISL-l, and through the winding of relay 251. to negative battery, If relay2L had operatedprior to relay 28, the operation of relay 281. would have been inhibited by normally open contacts ZSL-l.

Meanwhile, the subscriber at station set 200 has had the opportunity to determine whether or not this particular call is to be traced as a nuisance ,call. if he so decides, he sends a request signal tocircuit 210. For the purposes of this illustrative embodiment, this request signal may be symbolized by the closing of manual switch 220 which allows relay 2R to operate over'the path from ground through switch 220, make contacts 2SL-2, and through the winding or relay 2R'to negative battery. It is understood that other types of signaling may be used, such as dialing a predetermined digit.

The operation of relay 2R allows relay ZLU to operate over the path from ground through make contacts 2R-l, make contacts 2L-2, normally closed contacts 20R-3, and through the winding of relay 2LU to negative battery. Relay 21.0 is locked up to the ground applied to conductor S3 through make contacts 2LU-l'. Relay ZTRA is then operated over an obvious path. The operation of relay ZTRA causes contacts ZTRA-l through ZTRA-lO to apply ground to bridges 120 through 129, respectively. Closure of these contacts causes the gradual insertion of the bridges across the transmission paths of connectors 100 through l09 in the following manner.

Bridges 120 through 129 are identical and a description will only be given for bridge 120. Relay D having operated when station-set 200 went off-hook, transistor. 130 is in a nonconductive state with its base at the potential of negative battery and its emitter connected to negative battery through diode 131, conductor Tl, make contacts D-2, and the left-hand winding of relay A in connector 100. Ground is connected to the collector of transistor 130 through the right-hand winding of relay A, make contacts D-l, conductor R l, inductor I32, resistor 133, and diode 134. when ground is applied to the junction of resistors 135 and 136 by the closure of contacts 'ZTRA-l, no immediate change occurs because it is well known in the art that the voltage across a capacitor cannot change instantaneously and the potential on both sides of capacitor 137 was originally negative battery. Capacitor 137 gradually charges through the path from ground through contacts vTIRA-l, resistor 135, and through capacitor 137 to negative battery. This results in' the voltageat junction 1 38, and consequently? at the basef of transistor l3 0,.. g ra:dually becoming morepositive. The charging'of capacitor 137 therefore slowlylorward biases transistor 130, causing transistor- 130 to conduct, thereby gradually lowering the impedance in series with inductor 132, and resistor 133 and inserting the bridge across the transmission path of connector l00. This ZS and 2L, as shown by the following simulates the receiver off-hook condition of station set- 110 and maintains relay A in connector 100 operated, keeping the sleeve lead grounded to hold up the remainder of the connection. U v H v .t

The reader. will recall that bridges 120 through 129 "were simultaneously actuated by L, conta'c t:s,, @TRA-l through ZTRA-lll of relay -2TRA. ln thisillustrai ve embodiment, only connector 1001s involved in a nuisance call, it being understood that a nuisance call could be completed to station set 200 over any of connectors loofthrough 109. The other connectors are not involved in nuisance calls, but the customers;

tion of the bridges.

utilizing these connectors are notf disturbed because no acoustical disturbances are' introduced by-the gradual inser- Tuming back to Called CustomerSupervision Circuit 210, it can be seen that the operation of relay ZLU, through its make contacts 2LU-3; causes the bridge composed of inductor 211 and resistor "222 to be inserted across the called customer's line. This bridge, when inserted between conductors T3 and R3; simulates the receiver ofi-hook condition of the called line and causes relay D in connector 100 to be maintained in an operated state. The operation of relay D pro- ,,not operated, the proper polarity is not maintained across diodes 131 and 134 in bridge 120 and therefore transist'ofl30 will not conduct. In this case, bridge 120 will not mairitain relay A operated.

The subscriber at station set 200 may. now go on-hook without fear of releasing the connection. Furthermore, he may go olT-hook and originate another telephone call, as'follows.

When the'subscriber at station set 200 goes on-hook, relay 2L releases. Relay 20R then operates over the path from ground through normally closed contacts 2L-3, make contacts '2LU4, and through the winding of relay 20R to negative battery. Station set 200 is then cut off from connector due to break contacts 20R-l and MR4. The opening of break contacts 20R-4 in response to the operation of relay 20R removes relay 28 from the control of the ground of conductor S3 and relay 2S releases. Consequently, relay ISL releases when make contacts 28-1 in its path to ground open upon the release of relay 28. If the subscriber at station set 200 now goes off-hook in order to originate a call, relay 2!. is again operated, but this time in series with the line relay in the line circuit, not shown. Relay 20R remains operated over the path from ground through make contacts2L-3, normally closed contacts ZSL-3, make contacts 20R-5, and through the winding of relay 20R to negative battery.

As long as relay ZLU remains energized, relay ZTRA is energized and bridges through 129 remain across each of the connectors 100 through 109 that has its D relay energized. After completing the manual trace of the nuisance call, central office personnel will then release relay 2LU from control of the ground applied to conductor S 3. This will cause relay ZTRA to release and remove the ground from bridges 120 through 129, thereby turning ofi the transistors in the bridges and opening up the bridges. Circuit 210 is now restored to normal.

Accordingly, I have shown an arrangement whereby bridges may be gradually inserted across transmission circuits without creating any acoustical disturbances in the talking paths.

It is understood that the above described arrangement is merely illustrative of the application of the principles of this invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of my invention.

What I claim is:

l. Tln an arrangement for trapping telephone calls to a predetermined station in a step-by-step telephone switching system wherein 'a holding bridge is insertedacross the transiiiission path of a connector serving'said predetermined station upon receipt of a trap request signal from said station, the improvement comprising a transistor having its collector-t'o-emitter path serially connected to said bridge, and g,

a timing network connected to the. base of saidtransistor responsive 'to'said trap request signal for applying a changing voltage to said base over a predetermined timed interval whereby said transistor is forward biased over said interval.-

2. ln an arrangement for identifying the source of calls to a predetermined station in a communications system, apparatus I for inserting a holding bridge in a transmission circuit without a bridge of controllable conductivity including a transistor having its collector-to-emitter path connected to said transmission circuit,

timer means for increasing said conductivity from a predetermined minumum value to apredetermined maximum value including means coupled to the base of said transistor for biasing said transistor, and

starting means responsive to the receipt of a call by said station and said request signal for actuating said timer means.

3. The apparatus of claim 2 wherein said starting means comprises a really energizable in response to said request signal after said station has answered a call, and said timer means also comprises means responsive to the energization of said relay for actuating said biasing means.

4. The apparatus of claim 3 wherein said biasing means includes a capacitor coupled to the base of said transistor and means for charging said capacitor.

5. In an arrangement for identifying the source of calls to a predetermined station in a communications system, apparatus for inserting a holding bridge in a transmission circuit without creating acoustical disturbances comprising means at said station for transmitting an identification request signal,

a bridge of controllable conductivity connected to said transmission circuit including a transistor, an inductor, and a unidirectional current carrying device, said transistor having its collector-to-emitter path serially connected to said inductor and. said unidirectional current carrying device,

timer means for increasing said conductivity from a predetermined minimum value to a predetermined maximum value, and

starting means responsive to the receipt of a call by said station and said request signal for actuating said timer means.

6. The apparatus of claim 5 wherein said timer means includes a capacitor coupled to the base of said transistor and charging means responsive to said starting means for charging said capacitor.

7. The apparatus of claim 6 wherein said starting means includes a first relay operative in response to said station going off-hook during a terminating call to said station, a second relay operative in response to the operation of said first relay and the transmission of said request signal, and actuating means responsive to the operation of said second relay for actuating said charging means.

8. The apparatus of claim 7 further comprising means responsive to said actuating means for simulating an off-hook condition of said station and means responsive to said station going on-hook during a terminating call to said station for removing said station from sad transmission circuit and allowing said station to originate a call. 

1. TIn an arrangement for trapping telephone calls to a predetermined station in a step-by-step telephone switching system wherein a holding bridge is inserted across the transmission path of a connector serving said predetermined station upon receipt of a trap request signal from said station, the improvement comprising a transistor having its collector-to-emitter path serially connected to said bridge, and a timing network connected to the base of said transistor responsive to said trap request signal for applying a changing voltage to said base over a predetermined timed interval whereby said transistor is forward biased over said interval.
 2. In an arrangement for identifying the source of calls to a predetermined station in a communications system, apparatus for inserting a holding bridge in a transmission circuit without creating acoustical disturbances comprising means at said station for transmitting an identification request signal, a bridge of controllable conductivity including a transistor having its collector-to-emitter path connected to said transmission circuit, timer means for increasing said conductivity from a predetermined minumum value to a predetermined maximum value including means coupled to the base of said transistor for biasing said transistor, and starting means responsive to the receipt of a call by said station and said request signal for actuating said timer means.
 3. The apparatus of claim 2 wherein said starting means comprises a really energizable in response to said request signal after said station has answered a call, and said timer means also comprises means responsive to the energization of said relay for actuating said biasing means.
 4. The apparatus of claim 3 wherein said biasing means includes a capacitor coupled to the base of said transistor and means for charging said capacitor.
 5. In an arrangement for identifying the source of calls to a predetermined station in a communications system, apparatus for inserting a holding bridge in a transmission circuit without creating acoustical disturbances comprising means at said station for transmitting an identification request signal, a bridge of controllable conductivity connected to said transmission circuit including a transistor, an inductor, and a unidirectional current carrying device, said transistor having its collector-to-emitter path serially connected to said inductor and said unidirectional current carrying device, timer means for increasing said conductivity from a predetermined minimum value to a predetermined maximum value, and starting means responsive to the receipt of a call by said station and said request signal for actuating said timer means.
 6. The apparatus of claim 5 wherein said timer means includes a capacitor coupled to the base of said transistor and charging means responsive to said starting means for charging said capacitor.
 7. The apparatus of claim 6 wherein said starting means includes a first relay operative in response to said station going off-hook during a terminating call to said station, a second relay operative in response to the operation of said first relay and the transmission of said request signal, and actuating means responsive to the operation of said second reLay for actuating said charging means.
 8. The apparatus of claim 7 further comprising means responsive to said actuating means for simulating an off-hook condition of said station and means responsive to said station going on-hook during a terminating call to said station for removing said station from sad transmission circuit and allowing said station to originate a call. 